1. Field of the Invention
The present invention relates to a dynamoelectric machine such as an alternator or a starter motor, etc., that is mounted to an automobile, for example.
2. Description of the Related Art
First conventional generators include: a rotor that has field poles; a stator that includes: a stator core in which slots that number six times the number of field poles are formed at a predetermined pitch circumferentially; and first and second three-phase alternating-current windings that are each configured by delta-connecting three phase windings that have been wound into the stator core such that an electrical angle phase difference therebetween is 120 degrees; a rectifier that rectifies alternating-current output that is induced in the first and second three-phase alternating-current windings due to rotation of the rotor, which rotates synchronously with rotation of an engine; and a storage battery that is charged by rectified output from the rectifier, each of the phase windings being configured by connecting in series coil winding portions that have been wound into the stator core so as to have different electrical angular phases therebetween (see Patent Literature 1, for example).    Patent Literature 1: WO/2007/077236 (Pamphlet)
Hereinafter, three-phase alternating-current windings in which respective phase windings are configured by connecting in series two coil winding portions that have different electrical angular phases from each other, and that are configured by delta-connecting three phase windings such that the electrical angle phase difference between each is 120 degrees shall be designated “zigzag delta windings”. Furthermore, in the zigzag delta windings, three-phase alternating-current windings that are configured by rewinding the two coil winding portions that constitute each of the phase windings so as to be connected in series with matching electrical angular phase shall be designated “normal delta windings”. Moreover, generators that use normal delta windings in the first and second three-phase alternating-current windings are conventionally well known, and generators that use normal delta windings in the first and second three-phase alternating-current windings shall be designated “second conventional generators”.
In first conventional generators that use zigzag delta windings, because electromotive force phases of the two coil winding portions that constitute each of the phase windings are offset from each other, it is generally acknowledged that compound electromotive forces from the phase windings are reduced compared to electromotive forces from phase windings in second conventional generators that use normal delta windings. It is also known that armature reaction is less in the first conventional generators than in the second conventional generators.
When the relationship between offset of the electromagnetic force phases of the phase windings of the first conventional generators and magnitudes of armature reaction in the first and second conventional generators is considered, it is conventionally known that output from the rectifier (electric current) is reduced in the first conventional generators compared with the second conventional generators in a region in which the rotor rotates at low speed, and output from the rectifier is increased in a region in which the rotor rotates at high speed.
If the first and second conventional generators are used for automotive use, output from the rectifier increases as rotational speed (angular speed) of the rotor, which is synchronized with the rotation of the engine, increases until the rotational speed reaches a predetermined magnitude, but when the rotational speed of the rotor becomes higher than a predetermined speed, output from the rectifier is practically saturated.
If a vehicle is running at or above a predetermined speed, for example, the storage battery that is charged by the rectified output from the rectifier can supply sufficient electric power to drive items of electrical equipment that are being used in the vehicle because the rotor rotates at high speed. On the other hand, if the engine is rotating at low speed, such as when the engine is in an idling state, etc., output from the rectifier is small because rotation of the rotor is also at low speed. Because output from the rectifier in the first conventional generators in particular is lower than the output from the second conventional generators when the rotor rotates at low speed, there has been a risk that the storage battery may be flattened if the rotational speed of the rotor remains low.
It is possible that output from the rectifier could be increased even when the rotor rotates at low speed by increasing the number of turns in the phase windings to increase the electromotive force from the phase windings, but in that case resistance in the phase windings is increased and generating efficiency is reduced.
As a result of persistent diligent effort to solve these problems, the present applicants have found that output from a rectifier in a generator that uses zigzag delta windings can be increased when a rotor is rotating at low speed without having to increase the number of turns in the phase windings by setting the electrical angle phase difference between the first and second three-phase alternating-current windings appropriately, and have invented the present invention.